Syntheses, Crystal Structures, and Magnetic Properties of One-Dimensional Oxalato-Bridged Co(II), Ni(II), and Cu(II) Complexes with n-Aminopyridine (n = 2−4) as Terminal Ligand

Abstract

The reaction of M(ox) x 2H(2)O (M = Co(II), Ni(II)) or K(2)(Cu(ox)(2)) x 2H(2)O (ox = oxalate dianion) with n-ampy (n = 2, 3, 4; n-ampy = n-aminopyridine) and potassium oxalate monohydrate yields one-dimensional oxalato-bridged metal(II) complexes which have been characterized by FT-IR spectroscopy, variable-temperature magnetic measurements, and X-ray diffraction methods. The complexes M(mu-ox)(2-ampy)(2) (M = Co (1), Ni (2), Cu (3)) are isomorphous and crystallize in the monoclinic space group C2/c (No. 15), Z = 4, with unit cell parameters for 1 of a = 13.885(2) A, b = 11.010(2) A, c = 8.755(1) A, and beta = 94.21(2) degrees. The compounds M(mu-ox)(3-ampy)(2).1.5H(2)O (M = Co (4), Ni (5), Cu (6)) are also isomorphous and crystallize in the orthorhombic space group Pcnn (No. 52), Z = 8, with unit cell parameters for 6 of a = 12.387(1), b = 12.935(3), and c = 18.632(2) A. Compound Co(mu-ox)(4-ampy)(2) (7) crystallizes in the space group C2/c (No. 15), Z = 4, with unit cell parameters of a = 16.478(3) A, b = 5.484(1) A, c = 16.592(2) A, and beta = 117.76(1) degrees. Complexes M(mu-ox)(4-ampy)(2) (M = Ni (8), Cu (9)) crystallize in the orthorhombic space group Fddd (No. 70), Z = 8, with unit cell parameters for 8 of a = 5.342(1), b = 17.078(3), and c = 29.469(4) A. All compounds are comprised of one-dimensional chains in which M(n-ampy)(2)(2+) units are sequentially bridged by bis-bidentate oxalato ligands with M.M intrachain distances in the range of 5.34-5.66 A. In all cases, the metal atoms are six-coordinated to four oxygen atoms, belonging to two bridging oxalato ligands, and the endo-cyclic nitrogen atoms, from two n-ampy ligands, building distorted octahedral surroundings. The aromatic bases are bound to the metal atom in cis (1-6) or trans (7-9) positions. Magnetic susceptibility measurements in the temperature range of 2-300 K show the occurrence of antiferromagnetic intrachain interactions except for the compound 3 in which a weak ferromagnetic coupling is observed. Compound 7 shows spontaneous magnetization below 8 K, which corresponds to the presence of spin canted antiferromagnetism.

1D and 2D Cobalt(II) Coordination Polymers, Co(ox)(en): Synthesis, Structures and Magnetic Properties

“…The octahedral coordinate in zigzag chains can adopt terminal ligand positions by monodentate or chelating bidentate ligands, while linear chains can only adopt monodentate ligands. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] On the other hand, 2D layered structures contain bridging multidentate ligands such as 2,2'-bipyrimidine, pyrazine, and 4,4'-bipyridine (bpy), which are obviously different from chelating bidentate ligands found in 1D structures. [18][19][20][21][22][23][24][25] The geometric patterns of the layers are essentially distinguished by the facility and number of chelating ligands in the structures.…”

Synthesis, Structure, and Magnetic Properties of 1D Nickel Coordination Polymer Ni(en)(ox)·2H2O (en = ethylenediamine; ox = oxalate)

“…1 The octahedral coordinate in zigzag chains can adopt one of two terminal ligand positions: monodentate or bidentate. The infinite homometallic zigzag chains with terminal monodentate ligands are found in such as Co(ox)(im)2 (im = imidazole), 2 M(ox) (aquo)(L) (M = Cu, Co, Zn; L = purine, adenine), 3 [Zn(ox)2(py)]· H2O (py = pyridine) 4 and M(ox)(ampy)2 (M = Cu, Co, Ni; ampy = 2-aminopyridine), 5 whereas examples with bidentate ligands include M 2 (ox) 2 (bpy) 2 ·2H 2 O (M = Cu, Cd, Mn; bpy = 2,2'-bipyridine), 2,6 M(ox)(dpa) (M = Fe, Ni, Co; dpa = 2,2'-dipyridylamine), 7 Zn(ox)(en)·2H2O (en = ethylenediamine) 8 and [Cu(ox)(tmem)]·4H2O (tmem = N,N,N',N'-tetramethylethylenediamine). 9 Depending on orbital topology followed by the end capping ligands used in the synthesis, these compounds show ferromagnetic or antiferromagnetic couplings with various exchange coupling J values.…”

One‐Dimensional Oxalato‐Bridged Metal(II) Complexes with 4‐Amino‐1,2,4‐triazole as Apical Ligand

“…[9][10][11] This work aims (a) to develop standard synthesis routes (nature of reactants and synthetic conditions) to achieve a straight-forward design of one-dimensional oxalato-metal frameworks, (b) to study the influence of the structural features of these compounds on the magnetic interactions transmitted through the oxalato ligand, (c) to analyze the role of the terminal ligands in the type and magnitude of the crystalline interactions (essentially, hydrogen bonds and other non-covalent interactions between the aromatic systems of the pyridine rings), which ensure the cohesiveness of the crystal structure, and finally (d) to obtain analogous 1D systems with biological molecules such as nucleobases and other N-containing rings as terminal ligands. Indeed, our synthesis efforts have recently been successful with the isolation of a new family of 1D oxalato-bridged complexes in which the pyridinic bases are replaced by nucleobases such as purine and adenine, which behave as N-monodentate ligands.…”

“…The best-fitted values were J = +2.18 cm -1 , g = 2.16 and R = 2.0 × 10 -5 . The agreement factor R is defined as For oxalato-bridged Cu II complexes it has been found [9][10][11][12]20] that the value and type of the magnetic coupling is essentially governed by the magnitude of the overlap between the symmetry-adapted highest occupied molecular orbitals (HOMOs, σ symmetry) of the oxalato ligand and the metal-centered magnetic orbitals (mainly, a d x 2 -y 2-type orbital in square-pyramidal or tetragonally elongated octahedral geometries) which are defined by the short equatorial (or basal) copper-ligand bonds. The strongest antiferromagnetic coupling (values of J ranging from -260 to -400 cm -1 ) [12,20,21] result when the oxalato bridge is symmetrically coordinated with two short bonds to each copper() center in such a way that it is coplanar with the singly occupied molecular orbitals (SOMOs) of the copper atoms.…”

“…The strongest antiferromagnetic coupling (values of J ranging from -260 to -400 cm -1 ) [12,20,21] result when the oxalato bridge is symmetrically coordinated with two short bonds to each copper() center in such a way that it is coplanar with the singly occupied molecular orbitals (SOMOs) of the copper atoms. But when one copper-bridge distance is long (i. e., oxalato bridge is asymmetrically coordinated), the two metal-centered magnetic orbitals are parallel to each other and perpendicular to the bridging ligand (Scheme 1), the interaction between the d magnetic orbitals through the oxalato ligand is poor, and a weak anti-or ferromagnetic (when the overlap is zero, accidental orthogonality) [9][10][11]14,20,[22][23][24][25] coupling results, as occurs in 1.…”